We usually see the 5K50 mark on the valve body, which is general made of Bronze or cast iron. It’s a way of expressing nominal pressure and size by Japanese standards.
5K is shorthand of JIS 5K, which means the nominal pressure of the valve is 5kgf/cm2 or 0.5MPa. And 10K is the shorthand of JIS10K means the nominal pressure of the valve is 10kgf/cm2 or 1.0MPa.
And the number 50 behind of 5K means nominal valve size DN50, and generally will use 50A to expressing.
What is the meaning of JIS?
JIS is shorthand of Japanese industrial standard, for industrial valves and pipe steel, it has JIS B2220:2004(JPF/JSA), JIS B 2239, and JIS B 2240 standard.
It is important to note that different materials, sizes, and valve types correspond to different hydraulic test and leak inspection standards.
Bronze Globe Valve，5K-25A，Flanges as per JIS B2220 – 5K, means this bronze globe valve, nominal size is DN25， Nominal Pressure JIS 5K，Manufactured in accordance to JIS F7400, the hydraulic test of shell pressure is 15kg, for seat pressure is 8kg.
But if it’s Cast Iron Globe Valve, 5K-25A，Flanges as per JIS B2220 – 5K, same nominal size and pressure, but the hydraulic test of shell pressure should be 1.03MPa(kgf/cm2), and seat pressure should be 0.76MPa(kgf/cm2).
Moreover, If for Cast Iron Globe Valve, 5K-350A, means DN350 of this cast iron globe valve, the hydraulic test of shell pressure change to 0.88MPa(kgf/cm2), and seat pressure should be 0.65MPa(kgf/cm2).
One more thing that needs to be paid attention to is that the safety margin for selecting nominal pressure is significant. In the case of JIS 5K, the bronze globe valve can upper limit of 7kgf/cm2 in a static fluid at 120°C or lower. Generally, we recommended allowing a safety margin of 20% or 0.3-0.4 MPa, whichever is smaller for pressure, and a margin of about 25°C for temperature.